Goals inside the opening 13 minutes by Dean Hammond, from the penalty spot, and Gary Hart put the Seagulls firmly in control.
But a free kick by captain Kevin O'Connor (38) and an equaliser from Chris Moore three minutes into injury time kept the Bees' unbeaten start intact.
Something had to give after both teams opened the season with a couple of 1-0 wins and Brighton started like a house on fire.
Hammond sent Stuart Nelson the wrong way from the spot after Thomas Pinault had upended on-loan West Ham midfielder Tony Stokes just inside the penalty area.
Worse followed for Brentford four minutes later. Joel Lynch, Brighton's highly rated young centre-half, surged into the box before delivering a low cross to the near post which Hart poked into the roof of the net from point-blank range.
Brighton lost their way after that but Brentford did not look like scoring until O'Connor expertly curved a free-kick over the defensive wall and beyond keeper Wayne Henderson.
O'Connor's sweet strike changed the complexion of the contest as Brentford suddenly found fresh belief.
Andrew Frampton headed a free-kick from Sam Tillen straight at Henderson before the break and the visitors continued to threaten in the second half.
Frampton had a free-kick from 20 yards tipped over the bar by Henderson and substitute Alex Rhodes headed wide in the closing stages from a cross to the far post, shortly after joining the action.
Brighton were much less of an attacking threat after the break although Stokes and sub Dean Cox had shots saved by Nelson.
Jake Robinson also spurned the chance to set up Hammond, who was better placed when he shot tamely wide.
Brighton looked like seeing the game out until a long ball out of defence by Adam Griffiths went over the head of Adam El-Abd.
Moore nipped in to slot his second goal in as many games after his winner at Northampton four days earlier.